This invention relates to an inkjet printer head capable of thermal inkjet printing in which ink is heated to boil by applying an electric current to heating elements and ink droplets are ejected by the expanding force of bubbles formed in the ink.
One of the inkjet printers commonly used today are those capable of thermal inkjet printing in which ink is heated to boil by applying an electric current to heating elements and ink droplets are propelled and ejected by the expanding force of bubbles formed in the ink.
In order to heat the ink in thermal inkjet printing, an electric current needs to be applied to the heating elements for only a very brief period, so the printer head can be constructed in a comparatively simple design and precise printing is yet possible. In addition, the heating elements can be arranged on the substrate on a large scale and at high density. Because of these advantages, thermal inkjet printers are suitable for use not only at homes but also in commercial applications such as textile printing and on-demand printing where continuous printing is performed.
A disadvantage of the thermal inkjet printer head is that the heating elements are prone to be damaged by cavitation that occurs from the extinction of bubbles formed in order to eject ink droplets. In order to prevent this problem, the resistors in the heating elements are commonly protected by superposing an anti-cavitation coat. However, this is not desirable from the viewpoint of the need to achieve very rapid, almost instantaneous, transfer of heat from the heating elements to the ink since the protective coat placed between each heating resistor and the ink slows down the heating of the ink.
JP 9-174848 A proposes a heating element that does need to have a protective coat placed between the heating resistor and the ink in which bubbles are to be formed.
In JP 9-174848 A, thin-film resistors of a Ta—Si—O ternary alloy system having a thickness of 0.1 μm (1000 Å) with the constituent elements defined at proportions within a specified range are used as resistors in heating elements to enable the fabrication of an inkjet printer head that can be energized by application of as many as 108 impulses without being destroyed due to cavitation.
JP 2000-168088 A describes a thermal inkjet printer head that has a two-layered Ta—Si—O film about 7000 Å thick, with a self-oxidizing protective layer formed on top in a thickness of 100–500 Å. The head claims high durability against both cavitation damage and electrolytic corrosion.
As already mentioned, the thermal inkjet printers manufactured today are required to find use not only at homes but also as long-lived and highly durable commercial printers capable of continuous operation as in textile printing and on-demand printing. For use at homes, it has been necessary that the printer should be capable of withstanding the application of at least 108 impulses before the heating elements in the head become no longer operative. However, commercial printers that need to have better durability than home printers are required to use heads with much longer lives than those used on the home printers, for example, heads that can withstand the application of 1010 impulses.
However, the life of the heating elements proposed in JP 9-174848 A is only about 108 impulses and by no means exceeds 1010 impulses. Hence, the technology disclosed in JP 9-174848 A has the problem that it cannot manufacture an inkjet printer head that can withstand the application of 1010 impulses. The thermal inkjet printer head proposed in JP 2000-168088 has the same problem and its cycle life does not exceed 1010 impulses.